[Buildroot] [PATCH v4 2/4] autobuild-run: initial implementation of check_reproducibility()

[Atharva Lele]

For reproducible builds, we want to find out if there are any differences
between two builds having the same configuration, and to find the reason behind
them. The diffoscope tool looks inside different types of files to see where the
differences lie.

check_reproducibility() runs diffoscope on two output directories which are
expected in output/images and output/images-1. Since it uses objdump, it needs
to be provided the cross-compile prefix which is derived from the TARGET_CROSS
variable.

Since diffoscope may not be installed, we fall back to cmp for byte-by-byte
comparison. We add diffoscope to list of optional programs to avoid repeated
checking of its presence.

Signed-off-by: Atharva Lele <itsatharva at gmail.com>
Reviewed-by: Yann E. MORIN <yann.morin.1998 at free.fr>

---
Changes v3 -> v4:
  - Removed spaces on empty lines (suggested by Yann)
Changes v2 -> v3:
  - Use file size of reproducible_results to check reproducibility status, rather than
    exit status of cmp or diff (suggested by arnout)
  - Rename results file (diffoscope_output.txt -> reproducible_results) to avoid confusion
  - Change handling of diffoscope output text file using with open()
  - Changed commit message to have all necessary info (suggested by arnout)
  - Removed leftover code from when I was using an exception to handle
    diffoscope presense (thanks to arnout)

Changes v1 -> v2:
  - move diffoscope output to results dir (suggested by arnout)
  - fix make printvars call
  - Add diffoscope to DEFAULT_OPTIONAL_PROGS
---
 scripts/autobuild-run | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/scripts/autobuild-run b/scripts/autobuild-run
index 190a254..a053446 100755
--- a/scripts/autobuild-run
+++ b/scripts/autobuild-run
@@ -204,7 +204,7 @@ def get_branch():
 
 class SystemInfo:
     DEFAULT_NEEDED_PROGS = ["make", "git", "gcc"]
-    DEFAULT_OPTIONAL_PROGS = ["bzr", "java", "javac", "jar"]
+    DEFAULT_OPTIONAL_PROGS = ["bzr", "diffoscope", "java", "javac", "jar"]
 
     def __init__(self):
         self.needed_progs = list(self.__class__.DEFAULT_NEEDED_PROGS)
@@ -394,6 +394,43 @@ def stop_on_build_hang(monitor_thread_hung_build_flag,
                 break
         monitor_thread_stop_flag.wait(30)
 
+def check_reproducibility(**kwargs):
+    """Check reproducibility of builds
+
+    Use diffoscope on the built images, if diffoscope is not
+    installed, fallback to cmp
+    """
+
+    log = kwargs['log']
+    idir = "instance-%d" % kwargs['instance']
+    outputdir = os.path.join(idir, "output")
+    srcdir = os.path.join(idir, "buildroot")
+    reproducible_results = os.path.join(outputdir, "results", "reproducible_results")
+    # Using only tar images for now
+    build_1_image = os.path.join(outputdir, "images-1", "rootfs.tar")
+    build_2_image = os.path.join(outputdir, "images", "rootfs.tar")
+
+    with open(reproducible_results, 'w') as diff:
+        if kwargs['sysinfo'].has("diffoscope"):
+            # Prefix to point diffoscope towards cross-tools
+            prefix = subprocess.check_output(["make", "O=%s" % outputdir, "-C", srcdir, "printvars", "VARS=TARGET_CROSS"])
+            # Remove TARGET_CROSS= and \n from the string
+            prefix = prefix[13:-1]
+            log_write(log, "INFO: running diffoscope on images")
+            subprocess.call(["diffoscope", build_1_image, build_2_image,
+                                "--tool-prefix-binutils", prefix], stdout=diff, stderr=log)
+        else:
+            log_write(log, "INFO: diffoscope not installed, falling back to cmp")
+            subprocess.call(["cmp", "-b", "build_1_image", "build_2_image"], stdout=diff, stderr=log)
+
+    if os.stat(reproducible_results).st_size > 0:
+        log_write(log, "INFO: Build is non-reproducible.")
+        return -1
+
+    # rootfs images match byte-for-byte -> reproducible image
+    log_write(log, "INFO: Build is reproducible!")
+    return 0
+
 def do_build(**kwargs):
     """Run the build itself"""
 
-- 
2.20.1